Using a Transistor to Drive a Motor

A general-purpose bipolar junction transistor (BJT) usually drives low-current miniature DC motors. For example, a BC548 transistor may drive small loads of up to 5-volts requiring less than 300 mA.

Miniature low-current motors employed in consumer electronics products move the focusing lens in digital cameras, or provide vibration alert in mobile phones, and even spin the CD in CD players.

The BC548 has an absolute maximum collector rating of 500 mA, however, around 300 mA is the most one may use. In the circuit shown above, the diode D is a 1N4148 general-purpose component to protect the transistor from the back EMF of the motor coils.

The value of the base resistance RB depends upon the input switching signal. You may have a 3.3 V switching signal from a Raspberry Pi or Arduino, or perhaps a 5 V signal from a microcontroller. Please use the Transistor Base Resistor Calculator to find the precise value required for your application.

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